Under Cambodia’s criminal code, “entering into a secret agreement with a foreign state” is punishable by up to 30 years in prison and is equal to treason.

PHNOM PENH —

Kem Sokha, the leader of Cambodia’s opposition Cambodia National Rescue Party, was charged with “espionage” on Tuesday by a court in Phnom Penh.

The charge relates to a speech Sokha gave in Australia several years ago in which he talked about grassroots organizing against autocratic regimes.

Under Cambodia’s criminal code, “entering into a secret agreement with a foreign state” is punishable by up to 30 years in prison and is equal to treason.

The prosecution claimed that the video was evidence such a plot had existed since 1993.

“The activity that has continued up to now could be determined as an act of committing an obvious crime according to Cambodia’s criminal code. With this context, the arrest of Kem Sokha was made in accordance with the criminal code of Cambodia and in line with Article 80 of Cambodia’s constitution, and Article 12 of the law on the statutes of parliamentarians,” it said in a statement.

Sokha was arrested in a warrantless pre-dawn raid at his home in Phnom Penh on Sunday and was immediately sent to Trapaing Phlong prison.

In a statement on Monday, Australia and the United Kingdom joined the United States and the European Union in condemning the arrest.

The Australian Embassy said: “As a longstanding friend of Cambodia, Australia urges Cambodia to fully implement the principles of democracy as affirmed in the ASEAN Charter, and to respect freedom of expression, and peaceful assembly and association.”

In a separate statement, Mark Field, U.K. foreign and Commonwealth minister, said he was “greatly concerned” by the Cambodian government’s actions and urged Phnom Penh to take “immediate steps to restore prospects for a free and fair election in 2018”.

Suos Yara, the ruling party spokesman, claimed the case against Sokha was not a political issue. “This is the implementation of the law by the government and by the court, so the party didn’t interfere with this issue,” he said.

However, Sam Rainsy, a former Cambodia National Rescue Party president, said the “dictatorship” of Prime Minister Hun Sen would be brought down by ordinary Cambodians.

“The dictatorship in Cambodia ... cannot last long because through experience and history of all ages of the world, nothing can defeat the people,” he said.

Sokha’s lawyers have denied the charges against their client and said they would call on the court to drop the charges for lack of evidence.